In many wireless sensor networks techniques a cost effective location discovery technique is desirable. One such application includes a warehouse, where it is desirable to track the location of a large number of items efficiently. Many location estimation techniques for sensor networks are available in the art. These techniques can generally be divided into range based techniques and range free techniques. Range based location estimation techniques generally require an ability to make accurate pair-wise ranging measurements requiring costly infrastructure and hardware. Range free location estimation techniques, on the other hand, are generally considered cost effective.
One range-free location estimation technique known in the art utilizes proximity-based coarse location determination. This proximity technique estimates node location (transceiver location) by averaging the locations of anchor nodes or reference nodes (nodes with a priori location awareness such as devices placed at known positions on a map) within a communication range. Another range-free location technique, used for ad-hoc networks, counts the number of hops from node to every anchor to acquire coarse range estimation. Once the node has three or more range estimates, triangulation (multilateration) is used to estimate the node location. However, these known techniques provide very limited location estimation accuracy.
Another range free location estimation technique proposed in the art uses anchor nodes to form many triangular regions. A node is determined either inside or outside a triangular region. By combining these triangular regions, a node can be located by narrowing down the area where it can potentially reside. This technique has several shortcomings in that it requires a very complicated decision process, especially for 3-D location systems where a node's location estimation is highly dependent upon the distribution of its neighbor node. The triangulation technique is also inefficient for an irregularly deployed network.
Hence, there is a need for an improved range free location estimation method.